G. Brent Dawson

Title Assistant Professor Expertise Analytical Chemsitry, Bioanalytical separations, electroanalytical chemistry Education B.S., Furman University, 1995 Ph.D., Iowa State University, 2001 Postdoctoral Fellow, San José State University, 2001-2003 Office Sullivan Science Building, Rm 409 Phone 336.256.0069 E-Mail Email Dr. Dawson Group Website http://www.uncg.edu/~gbdawson/research.html

RESEARCH INTERESTS

We are focusing on the analysis of mixtures of peptides, proteins and pharmaceuticals by capillary electrophoresis.  In our work, we etch and modify the inner walls of the capillary to create a unique chromatographic surface.  Molecules can then be separated not only on the basis of their charge to size ratio (electrophoresis) but also their polarity.  Additionally, the capillary coating covers the highly polar silanol groups on the capillary wall thereby minimizing the tenacious adsorption of amine containing analytes.  This technique is called open tubular capillary electrochromatography.  Our goal is to develop it into a technique of choice for biological, pharmaceutical and clinical applications.

Development of novel capillaries
One project with many variations involves the characterization of the modified capillaries.  Capillaries are etched and their inner surfaces are coated with a monolayer of a stationary phase ligand. Test mixtures of peptides are analyzed under a variety of conditions and their separations are optimized.  Also, the changes in resolution, peak height and peak shape are examined as conditions such as electrolyte pH and acetonitrile concentration are changed.  Many of the capillaries are modified with ligands that show liquid crystal behavior in the bulk.  On these phases, we examine the temperature dependent resolution behavior to determine if this parameter can be better utilized in method development.

Optimizing fluorescent derivatization reactions
To make our test separations biologically relevant, we work at micromolar and submicromolar concentrations.  Due to the inherently short pathlength of the capillaries (25-75 μm) absorbance detection cannot be used.  Fluorescence detection exhibits very low limits of detection limits (~1 × 10-12 M) and can be readily interfaced to capillary based separation methods.  Few molecules are inherently fluorescent, but commercially available dyes react with functional groups on the analyte to create stable, highly fluorescent derivatives. 
One problem in this analysis scheme is the presence of multiple points of attachment for the fluorescent dye.  For example, proteins such as IgG antibodies contain 40-60 lysine groups where dye molecules can attach.  Incomplete derivatization reactions give products with electrophoretic behavior and impede detection and reliable identification of the analyte.  To overcome this problem we are working to develop ways to control the derivatization reaction to generate only one fluorescent derivative.  This project involves the MALDI-TOF mass spectrometer and biochemical methods such as tryptic digestion to determine the point of attachment of the fluorescent dyes. 

Interfacing electrochromatography with MALDI-TOF
One problem that all separations techniques suffer from is the lack of qualitative information given.  Chromatographic methods have overcome this problem by interfacing with electrospray mass spectrometry, and these techniques have been readily adopted by the pharmaceutical industry.  Capillary electrophoresis-based techniques have proven more difficult to interface with electrospray due to low flow rates in the capillary and incompatible background electrolytes.  Moreover, researchers have realized that many analyses would benefit from a separation that is ‘frozen in time’ that can be analyzed more thoroughly than those coupled to on-line electrospray.  Therefore we are beginning to develop off-line MALDI-TOF analysis of our electrochromatographic separations.
In this project, the liquid exiting the capillary must be deposited on a MALDI plate to generate a two dimensional record of the separation can be analyzed later.  Electrical contact must be maintained between the capillary and the plate and the plate must be then coated with matrix.  We are attempting to use a monolayer treated gold MALDI plate to specifically capture proteins of interest. 

REPRESENTATIVE PUBLICATIONS

Dawson, G. B.; Matyska, M. T.; Pesek, J. J.; Seipert, R. R.  Electrochromatographic studies of etched capillaries modified with a cyano pentoxy biphenyl liquid crystal.    Journal of Chromatography, A  (2004),  1047(2),  299-303.

Pesek, J. J.; Matyska, M. T.; Dawson, G. B.; Chen, J. I.; Boysen, R. I.; Hearn, M. T. W.  Open-tubular electrochromatographic characterization of synthetic peptides.    Electrophoresis  (2004),  25(9),  1211-1218.

Pesek, J. J.; Matyska, M. T.; Dawson, G. B.; Chen, J. I.; Boysen, R. I.; Hearn, M. T. W.  Open Tubular Capillary Electrochromatography of Synthetic Peptides on Etched Chemically Modified Columns.    Analytical Chemistry  (2004),  76(1),  23-30. 

Pesek J. J; Matyska M. T; Dawson G B.; Wilsdorf A.; Marc P.; Padki M.  Cholesterol bonded phase as a separation medium in liquid chromatography. Evaluation of properties and applications.    Journal of chromatography. A  (2003 Feb 7),  986(2),  253-62.